This invention relates to a sharpener for manual sharpening of the cutting teeth of saw chains for chain saws. The invention relates more particularly to such a sharpener wherein a depth limiter is disposed in front of the cutter in the cutting direction for controlling the depth of the cut. The cutter is defined by the line passing through a free surface forming the back of the teeth and a cutting face situated on the front of the teeth. A round file is provided for sharpening the cutter by cutting processing of the cutting face, the round file being adapted to the tooth front with the cutting face in cross-section.
For their optimum grinding power to be maintained, chain saws must be sharpened at regular intervals. In the case of chain saws with unsuitably sharpened cutting teeth of the saw chains, the saw chains do not run smoothly, the cutting power decreases and, in extreme cases, the saw chain may even break, which in turn may cause serious accidents. Moreover, the aforesaid disadvantages lead to high wear and failures of the engine driving the chain saw.
Grinding machines such as are used for grinding cutting teeth in the manufacture of saw chains cannot in practice be used in situ. Rather, it is customary, for sharpening cutting teeth, to use round files with a circular cross-section corresponding to the circular segment-shaped cross-section of the tooth front with the cutting face. With such files, the cutting teeth are reworked with the saw chain clamped on to the chain saw. Such saw chains, sharpened manually in situ, are reworked at fairly long intervals by means of stationary grinding devices, in order to restore their cutting geometry; but for this purpose the saw chains have to be removed from the chain saw. There are also automatic resharpening devices whereby the cutting teeth are resharpened with the saw chain clamped to the chain saw, the cutting teeth being conveyed past a manually applicable grinding element in their position on the smallest reversing radius of the driving wheel with a resetting device. However, saw chains thus sharpened display no stable straight cut.
Freehand sharpening of the cutting teeth by means of a round file calls for a high degree of skill on the part of the operator. Moreover, the geometry of the cutters is not maintained in this case.
A sharpening device of the above-mentioned type is known from German Utility Model DE-GM No. 17 90 678, in which a frame, consisting of two parallel guidance rods and two end sections, is movably guided in a clamping rail, the underside of which can be placed on the cutting teeth. Within the frame a round file is disposed movably parallel to the guidance rods, the round file can be swivelled around one of the guidance rods. In place of a round file a flat file can be inserted and used for the re-filing of the depth limiter. The sharpening angle can be pre-set in this known sharpening device by making the proper adjustment between the clamping rail and the guidance rods. The disadvantage in this known sharpening device is the fact that the sharpening of the cutting teeth on the one hand and the re-filing of the depth-limiter have to be made successively. This results in the cutting geometry not being maintained, since it is left up to the skill of the operator how closely the geometry of the delimiter is adjusted to that of the sharpened saw tooth during these successive filing steps.